1. Field of the Invention
The present invention relates to a magnetic recording apparatus and a positioning correction method in which a discrete track type magnetic storage medium provided with a discrete area is used. The discrete area includes plural tracks and a non-magnetic area located between the adjacent tracks. The track has a magnetic recording area in which data can be written and a non-magnetic area, and the data cannot be written in the non-magnetic area.
2. Description of the Related Art
Recently, as a storage capacity of a computer is increased, the storage capacity tends to be increased in the magnetic recording apparatus such as a hard disk drive (HDD). In order to achieve the large storage capacity of the magnetic recording apparatus, it is necessary to achieve a finer recording magnetic domain string in a magnetic recording layer to perform the high-density recording. The recording magnetic domain string is formed by a signal magnetic field generated from a magnetic head. A perpendicular magnetic recording method has been known as one of the high-density recording methods.
In the perpendicular magnetic recording method, the recording is performed by producing magnetization in a direction perpendicular to a recording layer surface of the magnetic recording medium. However, in the perpendicular magnetic recording method, when the recording density is not lower than 100 Gbit/in2, a writing operation to an adjacent track is performed by side fringing generated from a side face of the magnetic head, which results in a problem that a recording failure and a reproduction failure are generated.
Therefore, there is proposed a so-called discrete track type magnetic recording medium, in which the non-magnetic area made of a non-magnetic material is formed in a circumference direction of the recording layer of the magnetic recording medium and the data is recorded only in the magnetic recording area made of the magnetic material. According to the discrete track type magnetic recording medium, since the non-magnetic area is provided between the tracks, there is an advantage that the data can be prevented from being written in the adjacent track to realize good recording and reproducing characteristics.
Usually a composite head is used in the conventional magnetic recording apparatus. In the composite head, a recording head for writing the data in the magnetic recording medium and a reproducing head for reading the data from the magnetic recording medium are mounted on the same slider. In a rotary type drive structure, the composite head is supported at a leading end of a head actuator, the composite head is moved in a radial direction in which the composite head cuts across the track of the magnetic recording medium, and the composite head is controlled so as to be positioned at the desired sector. A servo area is provided at constant intervals in a track direction in a recording surface of the magnetic recording medium. Position information such as a track position and a sector position is recorded in the servo area.
A first portion whose surface is the effective magnetic recording portion and a second portion whose surface is not the effective magnetic recording portion are formed in the magnetic recording medium having the discrete track structure. The first portion is a projected magnetic area in which a magnetic film is provided. The second portion is the non-magnetic area or the recessed area in which the magnetic recording cannot be performed. That is, even if the magnetic film is formed in the second portion, the second portion is substantially formed as the non-magnetic area because the second portion is recessed.
In the magnetic recording medium having the discrete track structure, the servo area in which servo data is recorded can be embedded in the magnetic recording medium without using a usual servo track writer.
In addition to the sector and the track address, the servo data includes a servo pattern for detecting position deviation in the track (hereinafter referred to as “deviation detection servo pattern”). Examples of the deviation detection servo pattern include a burst type servo pattern and a phase difference type servo pattern.
One of modes of the phase difference type servo pattern is a pattern including straight lines oblique to the data track. According to a servo signal processing method, there are the mode provided with the unidirectional oblique pattern and the mode provided with both the forward oblique pattern and the reversely oblique pattern.
However, in the conventional technique, the servo pattern determined from a positional relationship between a rotation center of an arm and the head is embedded in the magnetic recording medium. Therefore, in the case where the ideal servo pattern previously assumed and the head are shifted from each other, sometimes the data cannot accurately be written and read because a head positioning center by the servo pattern is shifted from the center of the discrete track in which the data is recorded.
It is necessary that the center in positioning the head with the ideally embedded servo pattern, i.e., the tracking center coincide with the center of the discrete track in which the data is written and read. However, in the case where a transfer error is generated in transferring the servo pattern to a substrate during a magnetic recording medium production process, the tracking center does not coincide with the center of the discrete track, and the head is positioned while shifted from the center of the discrete track even if the head is in the tracking state. This causes the problem that sometimes the data cannot be written and read at the position where an error rate is lower than an allowable range.
For the phase difference type servo pattern provided with the servo pattern including the straight lines oblique to the data track, the servo pattern having an oblique angle determined from the positional relationship between the rotation center of the arm and the head is embedded in the magnetic recording medium. The shift is generated between the original head angle and the pattern angle by an influence of a head attachment error or the like, which results in the problem that the shift is generated in the tracking center.
For example, as disclosed in Japanese Patent Application Laid-Open No. 2000-123506, in order to correct the shift of the relative angle between the head angle and the pattern angle, the conventional phase difference type servo pattern is provided with the forward oblique pattern and the reversely oblique pattern to release the tracking shift using a servo signal in which the forward oblique pattern is reproduced and a signal in which the reversely oblique pattern is reproduced. This is because the influences of the opposite angle shifts emerge in the servo signal and the signal.
However, since two kinds of the servo patterns, i.e. the forward oblique servo pattern and reversely oblique servo pattern are provided in the conventional technique, an area of the servo area is increased compared with the normal magnetic recording medium, which results in the problem that the recording density of the magnetic recording medium cannot be improved.